Communication systems typically include a receiver that is configured to receive a signal transmitted from a transmitter. Jitter and/or noise can negatively affect the quality of a signal (signal quality) received by a receiver, and such an effect on signal quality can adversely impact the performance of a receiver in properly decoding a received signal. Signal quality can affect whether two network devices are able to communicate with each other. For example, a first network device may transmit a signal to a second network device to establish a link with the second network device. The second network device may determine quality of the received signal and based on the quality of the received signal send a response message back to the first network device. For example, if the quality of the received signal is less than a predetermined threshold, the second network device may not send a response message, or the second network device may send a response message indicating a link has not been established with the second network device.
Multiple techniques exist for directly or indirectly determining quality of a received signal. As a first example, a system may generate a received signal strength indication (RSSI) of the received signal, which is directly related to power (or strength) of the received signal. The higher the RSSI, the better the signal quality. As another example, the system may determine a signal-to-noise ratio (SNR). This includes determining a ratio between power (or amplitude) of a data signal and power (or amplitude) of noise on the data signal. A SNR may be measured statistically over an observation window to improve reliability of the measurement.
As yet another example, a system may perform an error vector measurement (EVM) to determine quality of a received signal. This includes observing constellation points of the received signal and quantizing differences between the constellation points and predetermined points to determine the quality of the received signal. A bit-error-rate (BER) may also or alternatively be determined to provide an indication of signal quality. The lower the BER, the better the quality of the received signal.
As a further example, a system may measure a characteristic in an eye-opening of an eye diagram to determine signal quality. An eye diagram can be created by overlaying traces of a signal having a non-repeating pattern. Characteristics of an eye diagram, such as width or height of the eye-opening of the eye diagram can be measured. Typically, the larger the eye-opening, the better the quality of the received signal. Measuring the size of the eye-opening is especially useful for systems using binary or quadrature amplitude modulation or frequency modulation, such as pulse-amplitude modulation (PAM) or frequency shift keying (FSK) modulation.